Because Windows does not recognise the external drives which results in code error 43 and Device Manager shows an exclamation mark against the appropriate USB Hub link nothing can be seen in Disk Management area. At 3.00 am today I connected one of the hard drives to my wife's W7 computer and copied across to her 2 TB external drive the contents Videos) then went to bed. I was up at 8.00 am and checked that all the files had copied across ok. My external drive showed up as drive F and drive H. Drive F is actually Drive C when it was in the now defunct Acer tower. Later today I am going to format that drive and use it as an external backup drive for the laptop. Of course this will only be feasible if the error 43 problem gets resolved.
Running the MS Fixit seemed to get rid of the alert in Device Manager - can you run that again then see if they are listed in diskmgmt.msc
If they are and you can assign them drive letters, see if the fix in that article will work for you.
I would just work with one HDD at a time.
While I'm not that deep into the hardware side of things, I would have thought that having two enclosures plugged in at the same time would have used more than one USB Hub, yet only one is showing an alert.
Failing that and given that S_G has the same problem with another Lenovo, I would suggest you raise this with Lenovo as the machine I assume, is still under warranty.